I've been struggling with this problem for... well, about a year now. Whenever I have taken my old Dell Inspiration 8600 (which is now in the hands of my sister) or IBM Thinkpad T41p onto a moving boat, the machines lock up periodically -- specifically, when I am using Adobe Photoshop CS. I used to think it was a RAM problem, but now I think it's related to the hard disk and the motion of the boat (or vibration of the engine). The Thinkpad I'm using has some sort of acceleration detection software that stops drive access when it detects anything out of the ordinary, but I have disabled it because it is too damn sensitive.
A friend on the last trip who had an iBook had his machine freeze for small periods of time while we were underway, but it always recovered moments later. There two other Windows machines on board that ran without problems as well. But both my Dell and IBM just freeze, requiring a hard reset. But when I am stationary, I have no problems and the machine is rock-solid. I do have both of the machines set up with the same software packages, and so must conclude that it is some problem with what I have installed and the motion/vibration of the boat/engine. It's bizarre, and it's pissing me off. I don't remember my older notebooks (Sony TR-1 and IBM Thinkpad A31) ever having this problem, but maybe my software configuration differed then.
Anyone have similar experiences? :)